1. Field of the Technology
The technology presented herein relates to a game apparatus and a storage medium storing a game program. More particularly, the present technology relates to a game apparatus which is operated by swinging an input device comprising an acceleration sensor, and a storage medium storing a game program.
2. Description of the Background Art
Conventionally, there is an apparatus which estimates a motion of a player's body. For example, Japanese Laid-Open Patent Publication No. 11-14395 (hereinafter referred to as Patent Document 1) discloses a movement data estimating apparatus for estimating the speed of a thrown ball when a player performs a throwing motion. The movement data estimating apparatus is a watch apparatus comprising an electronic circuit, an acceleration sensor, and two tilt switches. The movement data estimating apparatus, which is attached to a player's arm, estimates the speed of a thrown ball when a player performs a throwing motion. When a tilt switch has been in the ON state for a predetermined period of time, the movement data estimating apparatus determines a dominant hand of the player, depending on which of the tilt switches is in the ON state, and starts detection of an acceleration using the acceleration sensor. The acceleration sensor detects the absolute value of an acceleration occurring in the main body of the apparatus. The movement data estimating apparatus calculates an integral of the acceleration, and estimates the speed of a thrown ball based on the integral of the acceleration using an approximate expression indicating a relationship between acceleration integrals and actual speeds of the thrown ball as an estimation expression.
However, in the movement data estimating apparatus disclosed in Patent Document 1, since the value of the acceleration occurring in the main body of the apparatus changes significantly during a player's throwing motion, the tilt switches are provided in addition to the acceleration sensor so as to start measurement of the acceleration. Therefore, the cost of parts of the movement data estimating apparatus increases. Also, in the movement data estimating apparatus, since the integral is used to estimate the speed of a thrown ball, only an approximate speed of the thrown ball can be calculated, and a throwing direction or the like other than the speed cannot be estimated. Therefore, the movement data estimating apparatus estimates only the speed of a thrown ball, likely leading to the lack of enjoyment for the player. Also, the movement data estimating apparatus uses the integral so as to estimate the speed of a thrown ball, so that the motion cannot be estimated until the integration process is finished. Therefore, the movement data estimating apparatus cannot perform a process of reflecting a player's motion (e.g., throwing, etc.) in real time.